axios/lib/helpers/progressEventReducer.js

import speedometer from "./speedometer.js";
import throttle from "./throttle.js";

export default (listener, isDownloadStream, freq = 3) => {
  let bytesNotified = 0;
  const _speedometer = speedometer(50, 250);

  return throttle(e => {
    const loaded = e.loaded;
    const total = e.lengthComputable ? e.total : undefined;
    const progressBytes = loaded - bytesNotified;
    const rate = _speedometer(progressBytes);
    const inRange = loaded <= total;

    bytesNotified = loaded;

    const data = {
      loaded,
      total,
      progress: total ? (loaded / total) : undefined,
      bytes: progressBytes,
      rate: rate ? rate : undefined,
      estimated: rate && total && inRange ? (total - loaded) / rate : undefined,
      event: e,
      lengthComputable: total != null
    };

    data[isDownloadStream ? 'download' : 'upload'] = true;

    listener(data);
  }, freq);
}